Optical Element

ABSTRACT

The present invention relates to an optical element for use in a camera system for the inspection of passageways, a camera system for the inspection of passageways and a method of illuminating a passageway during inspection with a camera. An optical element for use in a camera system for the inspection of passageways comprises a first optical portion arranged to transmit light into a camera, a second optical portion arranged to transmit light emitted from a light source, the second optical portion located adjacent the first optical portion, and barrier means arranged to prevent light being transmitted from the second optical portion into the first optical portion.

CROSS-REFERENCE

This application is a continuation of co-pending application Ser. No.13/884,109, filed Jul. 18, 2013.

FIELD

The present invention relates to an optical element for use in a camerasystem for the inspection of passageways, a camera system for theinspection of passageways and a method of illuminating a passagewayduring inspection with a camera. In particular the invention relates toan optical element for protecting the video camera and the light sourceof a wellbore inspection system while permitting good illumination ofthe field of view of the camera.

BACKGROUND

In oil and gas wells, the wellbore may be open or may be clad with awell casing. Visual inspection of the wellbore is important to check theintegrity of the wellbore, and to investigate any downhole problems thatmay delay or prevent use of the well. For example, it is important toregularly inspect the casings for corrosion and wear.

Although visual inspection of the wellbore is important, the conditionstypically found in a wellbore tend to hinder the ability to use manycamera systems.

Wellbores can have diameters in the range 10 centimeters to 1 meter andcan reach depths of hundreds or thousands of meters. In order to inspectthese bores, therefore, it is not only necessary to provide a camerasystem that can operate at these depths, but also to provide thelighting required to be able to capture still images or video in thisconfined environment.

Furthermore, any camera system must be able to withstand the pressuresand temperatures encountered at depth in a borehole. Pressures at thesedepths can be very large and can reach around 150 MPa, and in addition,temperatures may exceed 100.degree. C.

Typically, downhole camera systems comprise a camera and light sourcecontained in a protective steel sheath. These camera systems are loweredinto the wellbore on an electrical cable or a shaft, with the imagesfrom the camera being relayed back to the surface where they aredisplayed and recorded.

The confined environment of the wellbore causes problems in designing acamera and lighting arrangement that is small enough while stilldelivering high enough light levels to capture the required images.

Several camera systems use a backlight system in which the light sourceis mounted at a distance behind the camera. The light is then directedinto the field of view of the camera by means of a reflector mountedadjacent to the camera. However, this approach is less successful innarrower passageways as the size of the camera becomes too largecompared to the diameter of the bore to allow sufficient light to bereflected.

It is also known to provide an array of light emitting diodes (LEDs) asthe light source due to their relatively low power consumption and smallsize. These LEDs are typically mounted around the outside of the cameraapproximately level with the camera lens. The LEDs therefore directlyilluminate the field of view of the camera.

In order to protect the camera and the light source from the harshenvironment of the wellbore, a cover or window is typically placed overthe distal end of the camera system. Any light emitted from the lightsource, therefore, must pass through this window before it illuminatesthe wellbore.

This has a disadvantage, however, because some of the light that travelsthrough the window is internally reflected and does not pass through thewindow.

Furthermore, some of the internally reflected light is directed backtowards the lens of the camera, leading to poor images.

It is an object of the present invention to provide an improved windowfor a subsea camera system that overcomes these problems.

SUMMARY OF THE INVENTION

According to the invention, there is provided an optical element for usein a camera system for the inspection of passageways, the elementcomprising: [0015] a first optical portion arranged to transmit lightinto a camera; [0016] a second optical portion arranged to transmitlight emitted from a light source, the second optical portion locatedadjacent the first optical portion; and [0017] barrier means arranged toprevent light being transmitted from the second optical portion into thefirst optical portion.

Also according to the invention, there is provided a camera system foruse in the inspection of passageways, the system comprising: [0019] ahousing having opposing first and second ends; [0020] a camera mountedin the housing, the camera positioned proximate the first end of thehousing; [0021] a light source arranged to direct emitted light out ofthe first end of the housing; and [0022] an optical element mounted atthe first end of the housing, the element comprising: a first opticalportion arranged to transmit light into the camera; [0024] a secondoptical portion arranged to transmit light emitted from the lightsource, the second optical portion located adjacent the first opticalportion; and [0025] barrier means arranged to prevent light beingtransmitted from the second optical portion into the first opticalportion.

Also according to the invention, there is provided a method ofilluminating a passageway during inspection with a camera system, thecamera system being according to the invention, and the methodcomprising the steps of:

-   -   illuminating the light source to provide emitted light;    -   transmitting the emitted light through the second optical        portion in a first direction to illuminate an object; and    -   transmitting light through the first optical portion in a second        direction, substantially opposite to the first direction, into        the camera so that the camera captures the image of the object;    -   wherein, in use, the emitted light is prevented from being        transmitted directly into the first optical portion from the        second optical portion by said barrier means.

Preferably, the barrier means comprises reflecting means to reflectlight in the second optical portion and to prevent light from the secondoptical portion being transmitted into the first optical portion. Thereflecting means may comprise a reflecting surface, which may comprise aperipheral surface of the first optical portion and/or the secondoptical portion.

In a preferred embodiment the barrier means comprises an interfacebetween the first optical portion and the second optical portion. Theinterface may be formed by an unpolished surface of at least one of thefirst and second optical portions.

In other embodiments, the barrier means comprises a gap between thefirst optical portion and the second optical portion. Preferably the gapis filled with silicone.

Preferably, the second optical portion surrounds the first opticalportion. The first and second optical portions may be concentric.Preferably, the first optical portion is cylindrical and the secondoptical portion is annular and surrounds the first optical portion.

Preferably, the first and second optical portions are made of sapphire.However, the first and second optical portions may be made of any othersuitable materials.

Preferably the optical portions are made of a ceramic material. Morepreferably the optical portions are made of quartz, diamond or crystal.

The optical element may be disc-shaped having parallel opposing firstand second end faces and the barrier means may be substantiallyperpendicular to the first and second end faces.

In preferred embodiments, the optical element further comprises a baseplate attached to the second end face. Preferably, the base plate ismade of titanium and the first and second optical portions are bonded tothe base plate by diffusion bonding.

When the optical element is mounted in a camera system, preferably thefirst end face of the optical element is closer to the first end of thehousing than the second end face, and the camera and the light sourceare located adjacent to the second end face.

Preferably the light source is arranged, in use, to illuminate anobject, the image of which is being captured by the camera.

Preferably, the camera system comprises a plurality of light sources.The plurality of light sources may comprise light emitting diodes.

Preferably, the plurality of light sources are arranged in a circlearound the camera.

In embodiments in which the optical element comprises a base plate incontact with the second end face, preferably the base plate includes atleast two apertures, and the camera and the light source are arranged sothat at least a part of each of the camera and the light source arelocated within an aperture.

Preferably the second optical portion is arranged to transmit light fromthe light source in a first direction through the optical element.Preferably the first optical portion is arranged to transmit light intothe camera in a second direction through the optical element. Preferablythe first direction is the opposite direction to the second direction.

The barrier means may prevent light from the second optical portiontravelling in the second direction being transmitted into the firstoptical portion.

Preferably the reflection means substantially maintains the light fromthe light source within the second optical portion as the light istransmitted from a second end of the second optical portion to a firstend of the second optical portion.

Preferably the second optical portion extends from a first end face ofthe optical element to a second end face of the optical element andtransmits light from the second end to the first end. Preferably thefirst optical portion extends from a first end face of the opticalelement to a second end face of the optical element and the camerareceives light entering from the first end and which is transmitted tothe second end of the optical element.

Preferably, the barrier means reflects light in the second opticalportion and prevent light from the second optical portion beingtransmitted into the first optical portion. The barrier means maycomprise a shroud. The shroud may locate around an outer peripheralsurface of the first optical portion and/or an inner peripheral surfaceof the second optical portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, andwith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an optical element for use in a camerasystem according to a first embodiment of the invention;

FIG. 2 a is a schematic diagram illustrating light reflection by aninterface present in the optical element of FIG. 1;

FIG. 2 b is a schematic diagram illustrating internal light reflectionby a front surface of an optical element when an interface is notpresent;

FIG. 3 is a perspective view of an optical element for use in a camerasystem according to a second preferred embodiment of the invention;

FIG. 4 is a sectional view of the optical element of FIG. 3;

FIG. 5 is a rear view of the optical element of FIG. 3 showing thearrangement of apertures in the base plate;

FIG. 6 is a cross-sectional view of the optical element of FIG. 3 withthe gap between the first and second optical portions exaggerated;

FIG. 7 is a cross-sectional view of a camera system including theoptical element of FIG. 3; and

FIG. 8 is an enlarged view of the front end of the camera system of FIG.7, showing the arrangement of the camera lens, light sources and opticalelement.

DETAILED DESCRIPTION

FIG. 1 shows a window or optical element 1 for use in a camera systemthat may be used to inspect wellbores or other passageways. These camerasystems typically include a camera and one or more light sourcesarranged to light the field of view of the camera. Typically these arehoused in a front, distal end region of an elongate cylindrical housingwhich is lowered down the wellbore by cables or a shaft attached at asecond end. In most cases, the camera systems will also include aviewport or optical element at the front end of the camera housing thatserves to protect the camera, in the harsh environmental of a wellborefor example.

In this embodiment the optical element 1 of the present inventioncomprises an optical layer 2 which includes an interface 4 whichprevents light emitted from a light source being internally reflectedwithin the optical element 1 back towards the camera.

The optical element 1 comprises a disc-shaped optical layer 2, which hasa first, inner optical portion 6 and a second, outer optical portion 8.The inner portion 6 is cylindrical, and the ring-shaped outer portion 8surrounds it so that an inner surface 10 of the outer portion 8 issubstantially in contact with the outer surface 12 of the inner portion6 thereby forming a cylindrical interface 4 between the inner and outerportions 6, 8.

The thickness of the inner and outer portions 6, 8 is the same so thatthe front and rear faces 14, 16 of the inner portion 6 are co-planarwith the respective front and rear faces 14′, 16′ of the outer portion8.

Preferably, both the inner and outer portions 6, 8 of the optical layer2 are made of sapphire, however, the optical layer 2 may be made ofquartz, diamond, crystal or any other suitable material. The material ofthe optical layer 2 must be optically clear, for example transparent ortranslucent, and must also be able to withstand the harsh conditionswithin a wellbore. For example, the optical layer must be able towithstand high pressures of over 100 MPa as well as high temperatures ofup to around 200.degree. C. The material should also be able towithstand any corrosive chemicals that are encountered in the wellbore.

n a simplest embodiment the cylindrical interface 4 extends for the fullthickness of the optical layer 2 and the plane of the interface 4 issubstantially perpendicular to the front and rear faces 14, 16 of thelayer 2. The inner and outer surfaces 10, 12 are unpolished so as tocreate a more optically reflective interface. When the optical element 1is installed within a camera system as described above, light entering acamera 20 is transmitted predominantly through the inner optical portion6, and the light emitted by light sources 22 is transmittedsubstantially through the outer optical portion 8. Due to the nature ofthe interface 4, emitted light travelling in a range of angles towardsthe central axis 18 of the apparatus is reflected by the interface 4 andis directed outwards, away from the central axis 18. This is shown mostclearly in FIG. 2 a. If the interface 4 was not present, then emittedlight travelling in the same direction, as shown in FIG. 2 b, would bereflected from the front surface 14 of the optical element 1 backtowards the camera.

The presence of the interface 4, therefore, has two importantadvantages. Emitted light that would otherwise be internally reflectedtowards the camera is now reflected outwards through the front face 14of outer portion 8 of the optical element 1. This means that, firstly,more light is available to illuminate the field of view of the camera,and in particular the walls of the wellbore passageway, and secondlyemitted light is prevented from being internally reflected into thecamera which would otherwise adversely affect picture quality.

FIG. 3 shows a second preferred embodiment of an optical element 100. Inthis example, the optical layer 102 is mounted on a base layer or baseplate 30. The base plate 30 is disc-shaped and has an outer diameterequal to the outer diameter of the optical layer 102. The thickness ofthe base plate 30 is significantly less than the thickness of theoptical layer 102, and in this embodiment the base plate 30 is about onequarter of the thickness of the optical layer 102.

The base plate 30 supports the optical layer 102 and includes aplurality of apertures 32,34 for receiving other parts of the camerasystem, as will be described in more detail below. In this example, thebase plate 30 is made of titanium, however, the base plate may be madeof any other suitable metallic material. Of importance in the selectionof material for the base plate 30 is the matching of the coefficients ofthermal expansion of the materials of the base plate 30 and the opticallayer 102. This is important as the optical element will be subjected toa large range of temperatures in use, for example −40.degree. C. to200.degree. C., and a mismatch of coefficients of thermal expansion maylead to cracking or at least de-bonding of the optical layer 102.

The base plate 30 and the optical layer 102 are bonded together so thatthe rear face 116 of the optical layer 102 is in intimate contact with afront face 36 of the base plate 30. In particular, in a preferredembodiment, a sapphire optical layer 102 is bonded to a titanium baseplate 30 by a process known as diffusion bonding. This process uses highcompressive forces and heat to bond the two materials at an atomiclevel. Preferably, a layer of aluminium 38 is introduced between theoptical layer 102 and the base plate 30 to act as a ‘glue’ and aid inthe diffusion bonding process. Other soft metals may be used to form thebond layer, however, the bond layer must be compliant.

The base plate 30 includes a larger central aperture 32 and severalsmaller apertures 34 arranged in a circle around the central aperture32, as shown most clearly in FIG. 5. The smaller apertures 34 are spacedequidistantly around the circle and in this example there are tenapertures 34. The central aperture 32 is sized to receive a lens of acamera that is mounted behind the base plate 30 when the optical elementis installed in a camera system, and the smaller apertures 34 aredesigned to each house a single one of a number of light sources thatare arranged to emit light to illuminate the field of view of thecamera.

The dimensions of the inner and outer portions 106, 108 of the opticallayer 102 are such that the central aperture 32 is aligned with theinner portion 106 and the outer apertures 34 are aligned with the outerportion 108 so that the interface 104 between the portions lies betweenthe central aperture 32 and the outer circle of apertures 34, as shownmost clearly in FIG. 4.

As shown in FIG. 6, in another preferred embodiment, the interface 204is in the form of a tapered annular gap 204 between the inner and outeroptical portions 206, 208. This tapered gap 204 is such that the outersurface 212 of the inner portion 206 and the inner surface 210 of theouter portion 208 are in contact at the rear face 216 of the opticallayer 202, but are spaced apart at the front face 214. The size of thegap 204 shown in FIG. 6 is exaggerated and typically the gap is minimaland primarily due to manufacturing tolerances between the inner andouter portions 206, 208 of the optical layer 202.

The gap 204 is filled with silicone which is preferably aerospace grade.In other embodiments other fillers may be used such as other grades ofsilicone, epoxies, rubbers or adhesives. Typically the choice of fillerwill be dependent on the environment in which the optical element willbe used. The gap 204 must be filled to prevent contamination reachingthe bond between the optical layer 202 and the base plate 230. This isparticularly important when aluminium is used to aid the bonding processdue to the relatively reactive nature of aluminium with many differentchemicals.

Further, in a preferred embodiment, the inner and outer surfaces 210,212 forming the interface 204 include a vapour deposition surfacecoating. This roughens the surfaces, further increasing the reflectivenature of the interface 204.

In other embodiments, the inner and outer surfaces 210, 212 forming theinterface 204 may be processed or treated in some other way to increasethe reflective nature of the interface 204. For example, one or both ofthe surfaces 210, 212 may be painted, or the surfaces may be textured bya process other than vapour deposition.

FIGS. 7 and 8 show the optical element 100 in place in the distal end 42of a camera system 40. The camera system 40 comprises a cylindricalhousing 44 which is typically made of stainless steel to withstand theoperating environment at depth in a wellbore. In addition to the camera120 and light sources 122, the camera system 40 may also include a powersupply, data transmitters and receivers, and controllers for controllingthe camera 120 and light sources 122.

Connectors 46 are located at one end of the cylindrical camera system 40for connecting to cables or a shaft used to lower the camera 40 down awellbore and also for permitting electrical connections to be made totransmit data back up to the surface.

The optical element 100 is located in a recess 48 in the distal end 42of the housing 44 at the opposite end to the connectors 46.

The camera is mounted directly behind the base plate 30 of the opticalelement 100 such that the lens of the camera 120 is aligned with thecentral aperture 32 in the base plate 30. The light sources 122, whichin this embodiment are light emitting diodes (LEDs) 122, protrudethrough the smaller apertures 34 such that at least a front portion ofthe LEDs 122 are within the base plate 30, as shown most clearly in FIG.8.

An O-ring 50 is used to form a seal between the optical layer 102 of theoptical element 100 and the internal surface of the housing 44. The useof a single optical element 100 having distinct inner and outer portionswithin an optical layer bonded to a unitary base plate means that only asingle high pressure seal is required to seal the entire optical element100 in the end of the camera system 40. If the two optical portions wereprovided by two separate optical elements, or if the optical layer wasnot securely bonded to the base plate, then a number of high pressureseals would be required within the camera system to provide effectiveseals around each of the components. This would take up valuable spacewithin the camera system and would decrease the available field of viewof the camera.

Although in the above-described embodiments the optical layer isdisc-shaped and comprises concentric inner and outer optical portionsthe optical layer may be of any suitable shape for use within a camerasystem. Furthermore, the second optical portion may not surround thefirst optical portion but, instead, the first and second opticalportions may be located side by side or in any other relative positionsdepending on the corresponding relative positions of the camera andlight sources in the camera system.

The optical element of the present invention, therefore, provides animprovement over existing camera system viewports by preventing unwantedinternal reflections while maximising the illumination provided by thelight sources and maximising the available field of view of the camera.

1. An optical element for use in a camera system for the inspection ofwellbore passageways, the element comprising an optical layer havingopposing first and second solid end faces, and the optical layercomprising: a first substantially clear optical portion arranged totransmit light into a camera, said first optical portion having opposingfront and rear faces; and a second substantially clear optical portionarranged to transmit light emitted from a light source, said secondoptical portion located adjacent said first optical portion and saidsecond optical portion having opposing front and rear faces, the frontfaces of the first and second optical portions being co-planar andforming said first end face of the optical layer, and the rear faces ofthe first and second optical portions being co-planar and forming saidsecond end face of the optical layer, wherein at least a portion of asurface of said second optical portion is in direct contact with atleast a portion of a surface of said first optical portion, and barriermeans between said first and second optical portions comprises aninterface formed by said contact, the barrier means being arranged toprevent light being transmitted from said second optical portion intosaid first optical portion.
 2. An optical element as claimed in claim 1,wherein said barrier means comprises a peripheral surface of said firstoptical portion and/or said second optical portion arranged to reflectlight in the second optical portion and to prevent light from the secondoptical portion being transmitted into the first optical portion.
 3. Anoptical element as claimed in claim 1, wherein said interface is formedby an unpolished surface of at least one of said first and secondoptical portions.
 4. An optical element as claimed in claim 1, whereinsaid interface is formed by a vapour deposited surface of at least oneof said first and second optical portions.
 5. An optical element asclaimed in claim 1, wherein said barrier means comprises a gap betweensaid first optical portion and said second optical portion.
 6. Anoptical element as claimed in claim 5, wherein said gap is filled withsilicone.
 7. An optical element as claimed in claim 1, wherein saidsecond optical portion surrounds said first optical portion.
 8. Anoptical element as claimed in claim 1, wherein said first and secondoptical portions are concentric.
 9. An optical element as claimed inclaim 1, wherein said first optical portion is cylindrical and saidsecond optical portion is annular and surrounds said first opticalportion.
 10. An optical element as claimed in claim 1, wherein saidfirst and second optical portions are made of sapphire, quartz, diamondor crystal.
 11. An optical element as claimed in claim 1, wherein saidbarrier means is substantially perpendicular to said first and secondend faces.
 12. An optical element as claimed in claim 1, wherein theoptical element further comprises a base plate attached to said secondface.
 13. An optical element as claimed in claim 12, wherein the baseplate includes a plurality of apertures.
 14. An optical element asclaimed in claim 12, wherein said base plate is made of titanium andsaid first and second optical portions are bonded to the base plate bydiffusion bonding.
 15. A camera system for use in the inspection ofwellbore passageways, the system comprising: a housing having opposingfirst and second ends; a camera mounted in said housing, said camerapositioned proximate said first end of said housing; a light sourcearranged to direct emitted light out of said first end of said housing;and an optical element mounted at said first end of said housing, saidelement comprising an optical layer having opposing first and secondsolid end faces, and the optical layer comprising: a first substantiallyclear optical portion arranged to transmit light into said camera, thefirst optical portion having opposing front and rear faces; a secondsubstantially clear optical portion arranged to transmit light emittedfrom said light source, said second optical portion located adjacentsaid first optical portion and said second optical portion havingopposing front and rear faces, the front faces of the first and secondoptical portions being co-planar and forming said first end face of theoptical layer, and the rear faces of the first and second opticalportions being co-planar and forming said second end face of the opticallayer; and wherein at least a portion of a surface of said secondoptical portion is in direct contact with at least a portion of asurface of said first optical portion, and barrier means between saidfirst and second optical portions comprises an interface formed by saidcontact, the barrier means being arranged to prevent light beingtransmitted from said second optical portion into said first opticalportion.
 16. A camera system as claimed in claim 15, wherein: said firstend face is closer to the first end of said housing than said second endface; and said camera and said light source are located adjacent to thesecond end face.
 17. A camera system as claimed in claim 15, wherein thecamera system comprises a plurality of light sources.
 18. A camerasystem as claimed in claim 17, wherein said plurality of light sourcescomprises light emitting diodes.
 19. A camera system as claimed in claim15, wherein the optical element comprises a base plate in contact withsaid second end face, the base plate including at least two apertures,and said camera and said light source are arranged so that at least apart of each of said camera and said light source are located within anaperture.
 20. A method of illuminating a wellbore passageway duringinspection with a camera system, the camera system being as claimed inclaim 15, and the method comprising the steps of: illuminating saidlight source to provide emitted light; transmitting said emitted lightthrough said second optical portion in a first direction to illuminatean object; and transmitting light through said first optical portion ina second direction, substantially opposite to said first direction, intosaid camera so that said camera captures the image of said object;wherein, in use, the emitted light is prevented from being transmitteddirectly into said first optical portion from said second opticalportion by said barrier means.